The invention concerns a method for reducing the size of polymer particles which absorb liquids to at least a certain extent, wherein the polymer particles are exposed to a liquid or to a damp atmosphere containing this liquid for a sufficient amount of time that the liquid penetrates at least into the region of the polymer particles proximate the surface.
The expression "polymer particle" means, within the current context, natural or synthetic thermoplastic, duroplastic or elastomer polymer particles obtained through polymerization, polycondensation or polyaddition, and which absorb arbitrary liquids to a certain extent.
Mechanical reduction in size of polymer particles of the above mentioned kind normally requires substantial technical effort and input of energy and is therefore expensive and time consuming. In addition, only those particles can be mechanically reduced in size which have a certain hardness and therefore a certain brittleness.
EP-A-0085014 describes a method for the reduction in size of elastic thermoplastic polymer particles such as polyethersulfone, polycarbonate or polysulfone. In this method, a solvent designated as a "tension split promoter", e.g. an acetone solution, diffuses into the surfaces of the polymer particles, wherein the structure of the particles is weakened along the diffusion path. The particles processed in this manner are subsequently subjected to an external mechanical force, e.g. a ball mill, wherein the coarse particles break up along the diffusion paths, defining lines of weakening, and smaller particles are obtained. The mechanical size reduction is therefore associated with a similar high energy input and high degree of technical difficulty and expense.
DE-A-2327956 describes a method for the production of water-soluble granulates containing hydratized salts, in particular granulated washing and cleaning agents. In order to obtain a granulate which does not bake together in bulk and which does not produce any hydratization heat, one uses a raw granulate containing a component suitable for hydratization while forming a product with a solid dry appearance (e.g. salts of polymer phosphoric acids, alcalicarbonates etc.) as well as water, wherein the water not only diffuses into the granulate but undergoes activated adsorption by effecting a change in the crystal water content of the water-soluble hydratized salts which are necessarily contained in the granulate. This raw granulate, of semi-solid damp manifestation, is expanded and solidified by microwave irradiation. There is no mention of reduction in size of the granulate.
Derwent abstract 81-69134 D of JP 56035928B discloses a method for the production of granulates made from powdered materials such as barium sulfate, aluminumsiliconoxide, instant coffee or powdered milk, wherein the powdered material is treated with a grid substance dissolved e.g. in water, ethanol or chlorated hydrocarbons which produces gas when heated, such as sodium hydrocarbonate or yeast and heated with microwave energy. The goal of this publication is to produce a granulate which is more porous than the initial powdered material for pharmaceuticals, food products etc. The initial powdered material should be wet with a sufficient amount of solution that it can evaporated in the microwave chamber. Granulation itself is done with conventional methods, wherein the microwave energy is solely utilized to drive out the gas producing substance. This publication also fails to mention any reduction in size of the granulate.
It is thereby the underlying purpose of the invention to propose a simple and economical method with the assistance of which polymer particles which absorb water to at least a limited extent can be reduced in size without using mechanical forces.